The Pleasure Instinct: Why We Crave Adventure, Chocolate, Pheromones, and Music (4 page)

Why does the infant pay attention to speech? It is surely not to learn the rules of syntax, widen its semantic base, or because it thinks language is an important mode of communication. No, the process of gazing into the eyes of those around it and eliciting motherese stems rather from the child’s basic, biological imperative to interact and connect emotionally with the people who nurture it. Infants orient toward the human voice, especially Mama’s, and lock on to her face, studying it with deep concentration. Why should they do this? What are the biological and psychological reasons for such persistent behaviors? Surely they are adaptive in that they draw the caretaker closer to the infant, allowing it to identify those who are most likely to offer affection and nurturance.

Babies continue to learn the sounds of their mother tongue during the first year of life, all the while maintaining their innate fondness for prosody and the other features of motherese. We will see in later chapters that the infant’s pleasure instinct for prosody has surprisingly long-term consequences, particularly for the evolution of aesthetic and musical preferences in the adult. For instance, synthesized sounds that have extreme pitch variations reminiscent of motherese evoke a feeling of pleasure in adults, who often associate them with happiness, interest, and surprise. Sounds that have a falling-pitch contour (high frequency decreasing to lower frequencies) elicit feelings of calm and relaxation. Imagine a parent who soothes a crying child with “Aahh,” or the meditation practitioner chanting “Ohmm.”Vocalizations that have a rising pitch contour have a very different effect; they tend to excite and grab our attention—“Hey!” From cross-cultural studies, it is clear that both natural and synthetic exaggerations in pitch have a universal appeal, whether they are embedded in music, speech, or song, presumably as a result of the same underlying biological mechanisms that have evolved to promote social attachment through our attraction to prosody.

An infant’s face also conveys emotional information directly to the caregiver, and they are incredibly talented mimics even at birth. Developmental psychologist Andrew Meltzoff was the first to demonstrate that newborns as young as forty-five minutes old are able to reproduce facial gestures corresponding to primary emotional conditions such as disgust (tongue protrusion), surprise (mouth opening), and sadness (lip protrusion)—even before they have seen their own face! Thus from the very beginning of life, human infants are busy employing and refining their methods of communication, and the primary topic of discourse is that of emotions.

While it is true that infants enter a linguistic babbling stage, a visual analog of this behavior is seen in their tendency to produce varied facial postures shortly after birth—another sort of babbling. Through trial and error, they learn quickly which expressions evoke an emotional response in adult observers. Adults, of course, learn the same lesson, and generate a number of facial postures and behaviors, eventually stumbling on the ones that elicit facial expressions in the infant that correspond to positive emotions. Emotions, then, are the first language we use. When an adult or an infant sees an emotional expression, it instantly gains information about the displayer’s current state. These talents translate to the linguistic domain, where squeaks, gurgles, and coos—the vocabulary of motherese—feed the emotional palate as well.

Studies have also shown that infants are born with a predisposition toward preferring abstract visual stimuli that look like human faces. Neonates a mere nine minutes old were shown different drawings before having ever seen a face—any face. They looked significantly longer (a common measure of preference) at a stylized pictogram of a normal human face, than at pictograms with exactly the same features but scrambled (a nose, mouth, eyes, and brows situated randomly on a circular “face”), suggesting they enter the world searching for kith and kin.

Just as prosody can be used as a pleasurable reward to condition infants, so too can the appearance of a human face. Newborns as young as two days old learn to alter their behavior (sucking and gazing) in order to maximize exposure to human faces. In fact, they master this task with astonishing efficiency, which tells us two very interesting things. First, neonates must be equipped with something that approaches single-trial learning, particularly when the task involves an evolutionarily significant variable such as the face. And second, the infant’s capacity for extracting emotional and intentional information from facial features has such critical importance for survival that the pleasure instinct has made the human face a most attractive and rewarding visual stimulus for babies (and, of course, adults).

We will find in later chapters that the human face has physical properties—such as lateral symmetry and exaggerated contrasts—in common with other stimuli that infants find naturally rewarding. Our evolved pleasure instinct for these visual features has lifelong repercussions for the development of aesthetics and physical attraction in the adult. Discovering which physical features the pleasure instinct nudges us toward during our first steps as neonates will help shed light on why certain aesthetic qualities, whether they are in faces, bodies, paintings, or landscapes, are universally appealing for humans. All of these inborn talents provide the neonate with tools for establishing an emotional communion with potential caregivers. One can hardly imagine the survival benefit to an infant who routinely engages inanimate objects (either through vocal or facial expressions) with no obvious human features, to the exclusion of their brethren. Nature is unwilling to take any chances with this most critical of objectives, the biological imperative to become attached to a caregiver, receive nurturance, and eventually become enmeshed into a broader social community. In the next few chapters, we will learn how this fundamental biological rule combines with embryological and developmental processes that regulate the growth and maturation of the human brain.

—Keller and Marian Breland,
The Misbehavior of Organisms

—Oscar Wilde,
The Picture of Dorian Gray

 

 

 

O
ne morning in 1970 a tortured twenty-four-year-old man with a history of drug abuse and severe depression walked into Dr. Robert Heath’s office at Tulane Medical School in New Orleans. By then Heath was a well-known, albeit controversial, figure who founded the Department of Psychiatry and Neurology at Tulane in 1948 after being recruited from Columbia University. Within a year of joining the faculty, Heath and his coworkers were conducting experimental studies in humans that would forever change the way psychiatrists think about emotions and at the same time provide enough source material to keep biomedical ethicists busy for decades to come.

By the time he was twenty-four years old, the patient known as B-19 had a diagnosis of temporal lobe epilepsy compounded by a history of chronic drug abuse and depression.“I live with the idea of suicide daily,” he is quoted as saying, and it is reported that he made several “abortive attempts.”We also learn that B-19 was homosexual and that “one aspect for the total treatment program for this patient was to explore the possibility of altering his sexual orientation through electrical stimulation of pleasure sites of the brain.”

During the early years of his tenure, Heath pioneered the therapeutic use of electrical stimulation of the brain (ESB) to treat epilepsy. Impressed by the work of Olds and Milner, who had just discovered “pleasure centers” in the brains of rats, Heath adapted their approach to recondition the brains of patients suffering from affective disorders and particularly schizophrenia.“The primary symptom of schizophrenia isn’t hallucinations or delusions,” he told a reporter years later.“It’s a defect in the pleasure response. Schizophrenics have a predominance of painful emotions. They function in an almost continuous state of fear or rage, fight or flight, because they don’t have the pleasure to neutralize it.” The idea was tantalizing—just stimulate the neural pleasure centers of a schizophrenic and this might rekindle damaged circuits affected by the disease and enable the patient to once again experience positive emotions.

Electrodes and cannulas (needle-thin tubes through which drugs may be delivered directly into the brain) were placed in fourteen subcortical structures of B-19’s brain, including the septal region, hippocampus, amygdala, and hypothalamus—areas that were hypothesized to regulate emotions in humans and had previously been identified as locations where rats “self-stimulate.”

Prior to the study, B-19’s “interests, contacts, and fantasies were exclusively homosexual; heterosexual activities were repugnant to him.”After B-19 recovered from the surgery, Heath and his coworkers stimulated each electrode briefly and asked their patient to report what he felt. Stimulation at most brain regions produced only mild or “neutral” feelings, and in some cases actually induced anxiety or other aversive sensations. But one electrode positioned in the septal region consistently produced an intense pleasurable response. “The patient reported feelings of pleasure, alertness, and warmth (goodwill); he had feelings of sexual arousal and described a compulsion to masturbate.”

During the first phase of treatment, B-19 was given a portable transistorized device that could be used to activate the different electrodes implanted in his brain.At first he experimented by stimulating a variety of sites—each time he pressed a different button, the device sent out a one-second pulse of electrical current to the corresponding electrode. Within a short time, however, the young patient was stimulating his septal electrode almost exclusively. During treatment sessions, he was permitted to wear the device for periods of three hours, and on one occasion stimulated this region more than fifteen hundred times (about once every thirteen seconds on average). During phase two of the treatment, B-19 was allowed to self-stimulate his septal electrode while watching “stag movies” of heterosexual activity, and he became “increasingly aroused.” Pleased with their patient’s progress, the innovative scientists hired a “lady of the evening” to assist them with phase three in which B-19 had his first “pleasurable” heterosexual encounter after being primed by five minutes of continuous septal stimulation.

ESB was used to treat hundreds of patients (not just at Tulane) through the 1970s, although with limited success in schizophrenics. An interesting observation was that patients suffering from depression or anxiety often rated septal stimulation as more pleasurable than patients without a mood disorder. At the time, it was believed that the stimulation was restoring the functioning of a weakened limbic system—a set of brain regions that regulate emotional valence in humans; however, this interpretation has been refined considerably in recent years. Neuroscientists now understand far more about the limbic system and how it communicates with neocortical structures during the expression and feeling of emotions. Most of what we know about the biology of pleasure began with an accidental discovery by two young scientists.

In many areas of science rapid advancement often comes from serendipitous discoveries. Working in a basement laboratory in 1954, newly doctored James Olds and graduate student Peter Milner were smoothing out the kinks of a study in which they were to implant electrodes deep into the reticular formation of rats. The German physiologist Rudolph Hess had recently shown that stimulation of the brain-stem regulates the sleep-wake cycle, and Olds believed that different sites within this region might selectively lead to either activation or inhibition of the neocortex, producing states of alertness or calm respectively.

During the first run of their experiment, each time the rat sniffed a particular corner of the square testing platform, Olds stimulated its brain, expecting that the activation would initiate the animal’s natural tendency to explore and visit other corners. Strangely, just the opposite happened—the rat returned again and again to the corner where it received the stimulation. Puzzled by this, the pair soon confirmed that the electrode had not been positioned correctly in the reticular formation, as thought, but rather landed in the septal region, a largely unexplored, phylogenetically ancient part of the brain.

Realizing they were on to something important, they quickly replicated their findings and developed another experiment where each rat was allowed to directly self-stimulate its septal region by pressing a lever in a testing chamber—a twist on the classical Skinner box, where rats learn to press a lever for access to food or water. To their surprise, this produced rapid learning of the lever press response, and their rats were willing to perform a variety of tasks to have access to this stimulation. In other words, a brief electrical pulse to the septum seemed to have very similar reinforcing properties to natural rewards such as food, water, and sex. In the fifty years since this original study, self-stimulation has been found to reinforce behavior at a number of distinct but related brain regions in the limbic system and across a variety of different species, ranging from goldfish to humans. The fact that this neural circuit (and its purported function) is conserved across such diverse species suggests that it is a phylogenetically older part of the brain, having evolved in an ancestor common to all of these groups.

Perhaps no other discovery in neuroscience has created such a torrent of experiments, conferences, publications, and additional questions. As the circuit continued to be charted by the early pioneers it became apparent that brain stimulation was not only rewarding, it was also drive-inducing, and thus became a tool for studying natural motivation. Yet the big question remained unanswered:What exactly does an animal experience when its septum is stimulated? Is it pleasure? Is it sexual in nature? Or is it a general state of arousal that amplifies the natural drives of an animal depending on the contextual cues that surround it? Clearly we can’t ask a rat for commentary, so we have to infer its inner state—whether we’re talking about motivation, drives, feelings, or some other operational term—from its behavior. As we shall see, this is never easy.